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A052620
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E.g.f. (1-x)^2/(1-3x+x^3).
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0
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1, 1, 8, 66, 768, 11040, 190800, 3845520, 88583040, 2295578880, 66098592000, 2093556326400, 72337863628800, 2707751497651200, 109153235884492800, 4714413247095552000, 217193790828478464000, 10631538129843671040000
(list; graph; refs; listen; history; internal format)
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OFFSET
| 0,3
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LINKS
| INRIA Algorithms Project, Encyclopedia of Combinatorial Structures 566
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FORMULA
| E.g.f.: (-1+x)^2/(1-3*x+x^3)
Recurrence: {a(1)=1, a(0)=1, a(2)=8, (n^3+6*n^2+11*n+6)*a(n) +(-3*n-9)*a(n+2) +a(n+3)=0}
Sum(-1/9*(-1+2*_alpha^2-2*_alpha)*_alpha^(-1-n), _alpha=RootOf(1-3*_Z+_Z^3))*n!
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MAPLE
| spec := [S, {S=Sequence(Prod(Z, Sequence(Z), Union(Z, Sequence(Z))))}, labeled]: seq(combstruct[count](spec, size=n), n=0..20);
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CROSSREFS
| Sequence in context: A083385 A188450 A121766 * A052669 A076527 A166815
Adjacent sequences: A052617 A052618 A052619 * A052621 A052622 A052623
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KEYWORD
| easy,nonn
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AUTHOR
| encyclopedia(AT)pommard.inria.fr, Jan 25 2000
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